Since PLO was first reported by Nordin in 1955, little epidemiological data on PLO has been reported[8]. Smith reported that the incidence of PLO was approximately 4–8 cases per million persons[9]. A previous systematic review of 338 cases worldwide revealed that the average age of PLO patients was 35.7 years old and the average BMI was 22.2 kg/m2. Ninety-two percent of patients developed clinical symptoms between three months prior and post-delivery[6].
In recent years, case reports and case series of PLO have gradually increased due to increasing awareness of this disease, but there is still little documented research PLO in China. The authors of these reports speculate that there might be a potentially higher incidence of PLO in China due to the adherence of Chinese people to the traditional custom of postpartum confinement[10]. Postpartum confinement means that the mother must strictly rest in a sealed room at home for one month immediately after giving birth. During the postpartum confinement period, the mother is not allowed to go out or open the window for ventilation. In Chinese traditional practice, postpartum confinement could help women recover better. However, the lack of exposure to ultraviolet sunlight may have a negative effect on the synthesis of vitamin D and bones, and increase the incidence of PLO[11].
Many studies have shown that PLO is a multifactorial disease with unclear pathogenesis. It has been suggested that genetic and endocrine factors play an important role in the development of PLO. Mutations in low-density lipoprotein receptor-related protein 5 (LRP5) have been found to be significantly associated with PLO[12–14]. Low-estrogen status after long-term anorexia, stress, excessive exercise and even premature ovarian failure, have been documented to be correlated with PLO[15]. Some studies have shown that increased calcium requirement for fetal skeletal development may also contribute to the development of PLO. At the end of pregnancy, fetal bone formation consumes about 30 grams of calcium, and more than 80% of calcium deposition occurs in the last trimester, which causes a sharp loss of maternal calcium and might lead to PLO during this period[16, 17]. In addition, low calcium intake, vitamin D deficiency, and use of glucocorticoids, heparin, and some anticonvulsants during pregnancy have also been suggested as risk factors for PLO[18–20].
Fractures may occur in patients with severe PLO, and the most commonly involved site is the lumbar or thoracic spine region[21, 22]. MRI is the most important examination to establish a definitive diagnosis. A typical MRI feature is strip-shaped abnormal signal area adjacent to the endplate in hypointense T1 and hyperintense T2 fat-suppressed phase[23]. It should be noted that different from postmenopausal osteoporotic fractures, PLO vertebral fractures often involve multiple vertebral fractures. In the present study, all PLO patients suffered vertebral fractures involving multiple vertebral fractures. This is consistent with the results of a previously published systematic review, reporting an average of 4.4 vertebral fractures among the 155 enrolled patients[6]. In view of this imaging feature, it is recommended that all PLO patients with vertebral fractures routinely undergo both lumbar and thoracic MRI examinations at the same time to rule out concurrent thoracolumbar fractures.
At present, there is still no consensus on the treatment of PLO, and the treatment protocol is mainly referred to that of postmenopausal osteoporosis. It is generally accepted that breastfeeding should be discontinued immediately after the establishment of a PLO diagnosis. Individualized drug treatment should be provided according to pain severity, bone density, bone remodeling markers, and re-pregnancy plan[24]. Currently, the commonly used drugs include calcium and vitamin D, calcitonin, bisphosphonate, teriparatide, denosumab, etc. Calcium and vitamin D can still be used as basic treatment. For patients with severe pain, calcitonin drugs can be considered due to its better analgesic effect in the short term[25]. Bisphosphonate has been widely used in the treatment of postmenopausal osteoporosis. However, since the drug will deposit in the bone tissue for a long time due to its long half-life, it remains unclear whether bisphosphonate will have an impact on the fetus during the second pregnancy. Therefore, for patients who may choose to have a second pregnancy, bisphosphonate should be carefully used[26, 27]. Teriparatide has a shorter half-life compared with bisphosphate and has been reported to have good clinical effect on PLO[28, 29]. Denosumab is also widely used and has achieved good results in the treatment of PLO. Although its half-life is longer than that of teriparatide, it is more convenient to use and has better compliance[30].
Although the symptoms in all six patients were relieved at the last follow-up date in this study, there were still four patients with residual low back pain of varying degrees, suggesting that the symptoms of PLO may take a long time to disappear. Kyveritakis evaluated the clinical prognosis of PLO patients during a 6-year follow-up period, and found that 58% of the patients needed more than 3 years for the complete relieve of clinical symptoms, and about 1/4 of the patients suffered refracture. These findings indicate that PLO may not be a simple self-limiting disease, and requires appropriate therapy[21].